Help with fitting at back please!

I could use a little help here sewing friends. I've successfully made a small bust alteration and feel really good about my muslin as far as that goes. However, the backside has some problems and I'm not sure whether to adjust the darts or adjust at the center back seam. I tried taking it in some along the center back seam, but that didn't seem to be the answer, so I took that back out. These pictures represent the seam sewn at 1/2" according to the pattern. Any suggestions? Thanks so much!